1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to an array substrate and a fabricating method thereof for a liquid crystal display device that implements In-Plane Switching (IPS) in which an electric field applied to liquid crystal is generated in a plane parallel to a substrate.
2. Discussion of the Related Art
Until recently, a cathode-ray tube (CRT) has usually been used for displays. However, flat panel displays are becoming more common because of their small depth, low weight and low power consumption. Thin film transistor liquid crystal displays (TFT-LCDs) are currently undergoing development to improve their resolution and to reduce their thickness.
Generally, a liquid crystal display device includes an upper substrate and a lower substrate each having an electrode thereon and liquid crystal interposed therebetween. If the liquid crystal is aligned by an electric field generated by a voltage applied to the electrodes, desired images can be displayed by a change of transmissivity that depends on the alignment direction of the liquid crystal molecules.
The general structure of a conventional liquid crystal display device will be described hereinafter with reference to FIG. 1. FIG. 1 is a cross-sectional view illustrating a structure of the conventional liquid crystal display device. As shown in the figure, a gate electrode 21 made of conductive material such as a metal is formed on a lower substrate 10, i.e., an array substrate. A gate insulating layer 30 including inorganic insulating material such as silicon oxide (SiO2) or silicon nitride (SiNx) is formed on the gate electrode 21 and on the lower substrate 10. An active layer 41 is formed on the gate insulating layer 30 using amorphous silicon. An ohmic contact layer 51, 52 is formed on the active layer 41 using a doped amorphous silicon. Source and drain electrodes 61, 62 made of conductive material are formed on the ohmic contact layer 51, 52 respectively. The gate electrode, the source electrode and the drain electrode constitute a thin film transistor “T”. A passivation layer 70 is then formed on the source and drain electrode 61, 62 using inorganic insulating material or organic insulating material. A contact hole 71 through the passivation layer 70 exposes the drain electrode 62 to the air. A pixel electrode 81 made of transparent conductive material is formed on the passivation layer 70. The pixel electrode 81 contacts the drain electrode 62 through the contact hole 71. A black matrix 91 is formed beneath a part of an upper substrate 90 corresponding to the thin film transistor “T”. A color filter 92 is formed beneath the black matrix 91. The color filter 92 has sub-color filters Red (R), Green (G) and Blue (B) arranged in a repeated order of R, G, B. A common electrode 93 made of transparent conductive material is formed beneath the color filter 92. In addition, a liquid crystal layer 100 is interposed between the upper and lower substrates 90, 10.
Liquid crystal molecules are aligned by an electric field generated perpendicularly to the substrates by a voltage applied to the pixel and common electrodes in the conventional liquid crystal display device. Characteristics such as a transmissivity and an aperture ratio are good in the conventional liquid crystal display device and, because the common electrode serves as a ground, destruction of a liquid crystal cell caused by static electricity can be prevented. However, the conventional liquid crystal display device has disadvantages such as a narrow viewing angle. Accordingly, an in-plane switching (IPS) mode liquid crystal display device has been suggested as an alternative to overcome the disadvantages such as a narrow viewing angle.